clang-format: Fix corner case in AllowShortBlocksOnASingleLine.

Before:
  template <int> struct A4 { A4() { }
  };

After:
  template <int i> struct A4 {
    A4() {}
  };

This fixes llvm.org/PR19813 (at least the part that isn't working as
intended).

llvm-svn: 209438